This invention pertains to a cylinder block for an internal combustion engine. More specifically, this invention pertains to an improved cooling arrangement for an engine cylinder block.
Reciprocating internal combustion engines typically have a cast cylinder and crankcase block formed with a plurality of parallel cylinder bores with their longitudinal axes coplanar. In other words, the block contains a line of cylinders, and in a V-block there are two banks of cylinders in a line. The cylinder bores are substantially identical to accommodate identical pistons each connected through a connecting rod to a crankshaft. The lower end of each bore accommodates a piston and its connecting rod, and the upper end provides the working and combustion volume of the cylinder. The upper surface of the block, sometimes called its top deck, is machined flat for sealing engagement with the cylinder head block (or head blocks in the case of a V-shaped engine).
The cylinder block is a body of intricate shape and formed with a cooling jacket defining passages for engine coolant (water, ethylene or propylene glycol and additives) to flow around the upper portion of the cylinder bores to remove extraneous combustion heat from them. In some engines, the cooling passages encircle the combustion region of each cylinder so that heat is removed from the full circumference of each cylinder. However, in an effort to reduce the size and weight of engines, some engine blocks have been designed without coolant flow passages between the cylinders. Engine blocks of this design are called siamese blocks because adjoining cylinders are formed in the block with a common wall and without a coolant flow passage separating them.
Engine designers often resort to siamese cylinder block construction to save engine compartment space when iron cylinder liners are to be used in a cast aluminum block. When the cylinder bore is enlarged to receive an iron or steel liner, the resulting aluminum web between adjacent cylinders is not thick enough for reliable coring and casting of a coolant passage.
Designers have worked to enhance the flow of coolant in the remaining coolant passage area to compensate for the lost cooling surface area between the cylinders. But siamese block engines often experience a hot zone at the top of each cylinder in the area between them where there is no coolant flow. Such hot zones can shorten the life of piston rings due to local micro-welding in the top piston ring groove and tearing of ring material. Thus, there remains a need for a way to better cool the intra-cylinder webs in the deck region of engine cylinder blocks and especially in siamese cylinder blocks.
This invention is applicable to engine cylinder blocks generally and is especially applicable to siamese cylinder blocks. In accordance with the invention, an engine cylinder block is provided with one or more small, highly efficient heat exchangers located in cylinder wall portions of the block, preferably at or near its top deck surface, with at least one end of the heat exchanger extending into a coolant passage in the block. The heat exchangers are heat pipes that in the case of a siamese cylinder block, for example, preferably extend across the width of the common cylinder walls from the coolant passage on one side of the cylinder line to the coolant passage on the other side of the line.
As is known, heat pipes comprise evacuated, closed end pipes or casings of suitable diameter and length that have an internal longitudinal wick and are back-filled with a suitable quantity of a liquid that undergoes repeated vaporization and condensation to transport heat. The pipe and wick structure are usually made of a high thermal conductivity metal such as copper. But beyond the thermal conductivity of their structural elements, heat pipes accommodate a large heat flux for their size because they utilize the repeated, cyclic vaporization and condensation of a substance like water with high latent heat of such phase changes in removing heat from the top deck region of the block between the cylinders and transporting it to the coolant in the adjacent passages. The porous wick permits the condensed water at the coolant end of the pipe to flow under capillary forces back to the hot portion of the pipe near the cylinder bore. Obviously, one or more pipes may be used in the hot region of the block, and the heat flow from a pipe may be bi-directional or unidirectional.
One or more heat pipes may, for example, be embedded in the deck region of the block when it is cast. Each heat pipe would be placed like a core in the mold or pattern when the block is die or gravity cast or formed by lost foam casting. Aluminum casting alloy envelops the copper tube heat pipe(s) in a suitable bond for heat transfer. In a preferred embodiment, a relatively long heat pipe is located in each common wall between adjacent cylinders so that the ends of the pipes extend into the coolant passages. Heat flows from the two cylinders into their intra-wall and the central region of the pipe. The heat flux evaporates the working liquid (e.g., water) in each pipe and the vapor flows bi-directionally to the ends of the pipe where it is condensed, giving up its latent heat through the pipe end to the coolant. The condensed liquid flows from both ends of the pipe through the wick structure back to the middle of the pipe to replace the liquid evaporated there.
In another embodiment, two or more heat pipes, each accommodating unidirectional heat flow, are placed around or between the cylinders with their low temperature ends in coolant passages.
In an alternative embodiment to casting the heat pipes in a cylinder block, a slot or groove may be cut across the deck of the block and the heat pipe(s) suitably bonded in the groove with a high thermal conductivity bonding agent.
Other objects and advantages of this invention will become more apparent from a detailed description of a preferred embodiment of the invention which follows. Reference will be had to the drawing figure which are described in the following section.